Pitch control for rotor blades



INVENTOR. y HAROLD HIRSCH H. HlRsCH FITCH CONTROL FOR ROLIOR BLADES Filed Sept. 26, 1945 Nov. il, l947.

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ATTORNEY axis of thisl latter hinge.

Patented Nov. l1, 1947 PITCH CONTROL FOR ROTOR BLADES Harold Hirsch, Buffalo, N. YA., asslgnor to Curtiss- Wright Corporation, a corporation ot 'Delaware Application September 26, 1945, Serial No. 618,622

4 claims. `(c1. 17o-160) The present invention relates to helicopter rotor blade assemblies and is particularly conf cerned with improved means for transmitting motion to the individual rotor blades for blade pitch adjustment.

This invention is particularly useful with helicopter rotor blade assemblies of the articulated type in which the blade is provided with a flapping hinge structure and a lead-lag hinge structure, each of these hinges being independently effective to permit the rotor blade a limited degree of motion for reasons now well understood in the art, In addition the rotor blades are arranged for movement in a direction to change the pitch or angle of incidence for control of the lift eilect and for translational control of the helicopter as a whole, Heretofore considerable difficulty has been encountered in providing motion transmitting means for blade pitch change 'where the blade is articulated. This diiliculty is due to the hinge structures, the kinematic couplingeiect thereof and the need for adequate strength in the members used to support 'the rotating masses.

In the above noted form of rotor blade articulation it has been the common practice tc arrange motion transmitting means in such manner that it necessitated complicated and heavy levers and links all of which had to be located externally of the blade hinge or articular assembly. The desired'function of such a complicated system is not easily obtained asit necessitates placement of the levers and links in an exposed, unprotected area, introduces losses in aerodynamic eillciency and involves considerable expense in manufacture .and maintenance.

The present invention is carried out by retaining the articulated type of rotor blade, in which the flapping link and the lead-lag link are separate parts of the assembly, and arranging the motion transmitting system internally of the articulated links. In so doing, the internal parts of the motion transmittingsystem areprovided with a universal joint,y one axis ofwhich is arranged to be coincident with the axis of the leadlag link hinge when the rotor is operating at its optimum condition. At the same time a motion transmitting 1ink provided between the usualY swash plate and the rotor blade is operatively connected to the internal parts ofthe system at a zone adjacent the axis of the fiapping'link hinge so that'the end of the link directly connected to the swash plate intersects'the projected operating conditions the motion transmitting Thus for optimum system will be effective t`o 'maintain blade pitch settings during blade motion about the respective hinge axes. Accordingly, it is an object of this invention to overcome the noted objections of prior rotor blade pitch `changing means by incorporating the same within certain parts of the rotor blade connecting assembly.

v It is also an object of this invention to provide simple and light weight motion transmitting means for rotor blade pitch control which can be incorporated in the flapping and lead-lag hingeV structures of the blade assembly.

A further object resides in the arrangement of rotor 'blade pitch control means for' protective enclosure in the rotor blade retention means and in the incorporation of` a universal connection at the lead-lag hinge axis so that substantially no interference can result in the blade pitchv means or in the free action of the hinge structure.

Still another object may be found in the general arrangement of the motion transmitting means with respect to the blade hinge structures so that at normal. operating settings of the blades there Will be substantially no bladelfeathering effect While at operating conditions other than normal the blade feathering eiect can be reduced to an insignicantfactor.

Other features and objects of the present invention will be pointed out in the detailed description hereinafter to be given in connection l with the preferred form of the same as illustrated in the accompanying drawing, in which:

Figure l is a top plan view of only so much of one typical rotor blade assembly as will serve to indicate the arrangement and construction of themotion transmitting meansfor blade pitch control; and

Figure 2 is an enlarged, partial sectional detail,

in elevation, of the assembly as seen along line 2-2 of Figure 1.

In 'the drawing the preferred rotor blade assembly includes a hub structure I0 arranged with laterally projecting boss structures II `for the attachment of a -plurality of rotor blades. In Figure 1 only Ionerotor blade assembly has been shown ln detail as it is obvious that the remain- ;ingblade assemblies will be identical in all respects. This hub structure is carried on a vertical drive shaft I2 in the well known manner.

The typical rotor blade assembly illustrated is comprised of a pair of hinged links I3 and I4, a tubular elementv I5 carried by the 1ink I4, a pair of cooperating blade attachment fittings IB and I1 and' the rotor blade I8. Link I3 is of hollow tions 2II forattachment to the hub boss II by means of a pin 2i journaled in the boss and inv needle bearings 22 in the link furcations (Figure 1). Thus link I3 can move or hinge about the pin 2| in a vertical plane within the limits imposed by the upper stop boss 23 formed on one furcation 20 and the lower stops 24 formed on the hub boss II. Link I3 forms the flapping link member of the system above referred to.

The outer bifurcated end 26 of the link I3 is suitably formed to receive a hollow hinge pin 21, the axis of which is generally directed at right angles tothe axis of the hinge pin 2I. It should be understood that either or both of these hinge pins can be mounted at diilerent angles from that shown depending upon the desirability of having the rotor blades function in a manner different from that expected with the varrangement disclosed. Whatever the angular arrangement may be for the respectivel hinge pins the fui-cations 28 of link I4 are supported on bearings Y29 for hinging movement about the axis of the hinge pin 21. Thus the link I4 constitutes the lead-lag link for the blade I 8.

In the present, assembly the lead-lag link I4 carries a series of radial-thrust bearings 3l and a further needle bearing 32 for the mounting of the tubular element I5. 'I'he latter element projects outwardly of the link I4, and carries the fitting I6 to which the cooperating tting I1 is suitably aiiixed by bolts 33 in any well known manner. In turn the tting I1 is xed to the blade spar member 34 so that 'forces developed when the blade is rotated will be transmitted inwardly through the assembly just described to the element I5. Element I is provided with a threaded collar 35 which can be adjusted to determine the longitudinal position oi.' the element within the link I4 and at the same time Y bear against the thrust bearings 3l to transmit of the character described are made by rotating the tubular element I5 relative to the lead-lag link I4 in which it is mounted. Thus the inner reduced end of the element I5 is bifurcated at 4 the thrust collar 3B on element Il will prevent tension loads being imposed on the universal joint ll., Y'

vThe drive member 4I is adapted to be rotated by means oi.' a link B8 which is rigidly connected at one end to the arm 43 and at the opposite end to a blade pitch control system (not shown).

The 4control system. while not shown here, is

' understood to include a swash plate or equivalent agency together with means for eecting either group or cyclic pitch changes or both types of pitch changes of the rotor blades, The important portion of this complete control system is fully disclosed and includes the means for transmitting motion from the swash plate to the rotor blades through the hinged links I3 and I4. This above described system is believed to be a new and highly practical arrangement and accordingly constitutes the principal feature of the present invention. In a construction of the type described the assembly of the motion transmitting means internally of the links I3 and I4 will effectively nullify the kinematic coupling eiiect which otherwise imposes blade feathering motion upon the desired cyclic and/or group pitch settings if the universal joint is not greatly displaced from operative coincidence with the hinge axis of the lead-lag link. This condition will be satisiled easily according to the present invention whether the hinge axes are rectilinearly associated, as shown, or are directed at skewed angles.

.Moreoven this invention, when applied to a skewed" axis articulated rotor blade, will effectively prevent increase of blade feathering motion by the pitch adjusting means as a result of the kinematic coupling action of the hinged links.

31 to provide one yoke itting for a universal joint 38. This yoke end 31 extends through an aperture 39 in the tubular hinge pin 21 and is secured to a second yoke `end 4U formed on a drive tube 4I extending through the flapping link I3. 'Ihe drive tube ismounted for rotation in bearing 42 and is provided with an upwardly extending arm 43 which passes outwardly of the link I3 between the furcations 20. It is to be noted that the arm 43 has considerable latitude of movement between the link fur'cations so that an adequate degree of rotation of the drive member or tube can be had.

The yoke end 4U of drive member 4I passes into the hollow pin 21 through aperture 44 where it is joined to the cooperating yoke 31 by means of the usual swivel block 45 and pins 46 and 41. The pin 41 secures this universal joint in assembly by reason of its insertion through the pin 48 as is common practice. Inactual practice the pin 41 of the universal joint 381s movable to either side of coincidence with the axis of hinge pin 21 through less than 10 degrees in order to In the assembly and arrangement of the present motion transmitting means it will be noted that the link 58 is formed to have an offset and downwardly angling portion such that its free end intersects the projected axis X-X of the ilapping hinge pin 2| (Figure l). This particular positionment of the link 50 is arranged to occur when the rotor is operating at its best or optimum condition. When so positioned the flapping action of each blade assembly will not be accompanied by resultant motion of the link 50 and hence the blade will hold its selected pitch angle. Concurrently with the attainment of the link setting as above noted, the universal joint 38 ismade to assume its best position, with the axis of pin 41 coincident with the axis of the hollow leadlag hinge pin 21. Thus leading and lagging motion of the blade I8 cannot introduce any change in the angle of pitch.

For blade pitch settings less than orV greater than the normal as above noted, a slight blade feathering action is introduced but such action does not develop a. condition having any s'ubstantial adverse eiect on the characteristics of the blade operation and hence may be disregarded for all practical purposes.

.Theforegoing description has been devoted to the disclosure of one preferred and practical helicopter rotor blade assembly and pitch control transmitting means. It should be clear that identical assemblies are to be used for each blade whether there be one or more. 'I'he advantages attendant upon the improved motion transmitting means for rotor blades are simplicity of construction, adequate protection due to interior positionment of the operating parts, a clean rotor assembly, and eiective blade pitch control with negligible feathering action for settings above or below a normal pitch angle. In attaining these advantages the link 50 should be arranged so that its end which connects with the swash plate (not shown) intersects or is never far from intersection with the projected axis X-X of the flapping hinge pin 2|, and the universal joint 38 must lie on the axis of the lead-lag hinge pin 21.

It is assumed, of course, that modications may be made herein and that equivalent means can be utilized for that shown Iwithout departing from the spirit and intended scope of the claims annexed hereto. f i

What is claimed is:

1. In an aircraft sustaining rotor assembly having blades provided with a hinged apping link and a lead-lag link hingedly connected to the apping link, the flapping hinge being spaced radially of the rotor assembly from the lead-lag link hinge, a pitch adjusting mechanism for each rotor blade including a drive member rotatively mounted in the apping link, an element operatively carried in the lead-lag link and to one end .of which the blade is attached, a. universal joint operatively interconnecting one end of said drive member with the opposite end of said element, said universal joint having an axis which is movable to either side of a normal position of coincidence with the axis of the lead-lag hinge connection, and an operating link connected to said drive member for rotating the same whereby said element may be operated through said universal joint to adjust the rotor blade pitch.

2. In an aircraft sustaining rotor assembly having blades provided with a hinged flapping link and a lead-lag link hingedly connected to the flapping link, the flapping hinge being spaced radially oi the rotorassembly from the lead-lag link hinge, a pitch adjusting mechanism for each rotor blade including a drive member rotatably mounted in the flapping link, a crank arm on said drive member which extends outwardly of the ilapping link. an element operatively carried in the lead-lag link and to one end of which the blade is attached, a universal joint operatively interconnecting oneend of said drive member with the opposite end of said element, and an operating link connected to the outwardly extending end of said crank arm for rotating said' drive member whereby said element may be operated through flapping link, a pitch adjusting mechanism for each rotor blade including a drive member movably mounted in the flapping link, a crank arm on said drive member which extends outwardly of the ilapping link, an element operatively carried in the lead-lag link and to one end of which the blade is attached, a universal joint operatively interconnecting one end of said drive member with the opposite end of said element, said universal joint having an axis which is movable to either side of a normal position of coincidence with the axis of the lead-lag hinge connection, and an operating link 'connected to the outwardly extend- .ing end of said crank arm for moving said drive member whereby said element may be operated through said universal joint to adjust the rotor blade pitch, said operating link having one end arranged for movement to either side of a normal position intersecting the projected axis of the flapping link hinge.

4. In an aircraft sustaining rotor assembly having blades provided with a hinged flapping link and a lead-lag link hngedly connected to the napping link, a pitch adjusting mechanism for each rotor blade including a drivemember rotatively mounted in the flapping link, a crank arm on said drive member which extends outwardly of the apping link, an element operatively carried in the lead-lag link and to one end of which the normal position intersecting the projected axis of said universal Joint to adjust the rotor bladeV pitch, said operating link having one end arranged for movement to either side oi' a normal position intersecting the projected axis of the napping link hinge.

3. In an aircraft sustaining rotor assembly having blades provided with a hinged apping link and a lead-lag link hingedly connected to Athe the flapping link hinge.

" HAROLD. HIRSCH.

REFERENCES CITED The following references are of record in the ille of this patent:-

Focke Jan.'1 1, 1944 

